improve UX for user without workspace

[fey]

Problem description

When a user first logs in, they have no information on where to go. In some browsers, the top bar is blocked by password managers, so it's unclear where to go next.

Proposed solution

If the user doesn't have a workspace, we display on the page https://fixit.hexlet.io/workspaces a censored block with a call to action and a link to the page of creating a workspace. Examples of such blocks: https://getbootstrap.com/docs/5.2/examples/heroes/